Space Station Designer · published
Welcome to the sixteenth Dev Diary entry of 'Space Station Designer'! Today, we're looking at the real-world science and history behind one of humanity's boldest concepts: the Space Elevator.
The space elevator isn't a modern science-fiction invention. Here’s how it started:We know Konstantin Tsiolkovsky as the Russian ‘father of rocketry’, because he figured out the ‘Rocket Equation’ way before modern rockets existed. It happened that he visited the newly constructed Eiffel Tower at the 1889 Paris Universal Exposition, where inventors and engineers showcased their latest designs.
Konstantin Tsiolkovsky - Soviet postal stamp of 1986At 312 meters tall, the Eiffel Tower was the tallest man-made structure on Earth, an incredible feat for 1889! Before its construction, many engineers feared that a metal tower of that height would simply be snapped in half by violent high-altitude winds. It still stands today.
Eiffel Tower as in 1889
Tsiolkovsky, quite obsessed with space-related topics, could not help having that thought: ‘What if we just kept building up until the tower reached past the atmosphere and into space?’ Remember that back then, there were only very crude powder rockets, for fireworks or military use, and no guidance mechanisms. So the idea of a ‘tower to space’ wasn’t that crazy, all things considered.It turns out that the modern concept of Space Elevator also came from Russia (at that point Soviet Union), in 1960. It was the work of Engineer Yuri Artsutanov. But Sputnik had been sent into orbit 2 years ago, and the R-7 rocket had a reasonable success rate. So the article was seen as an interesting curiosity, but not as something immediately useful.
Modern Space Elevator concept
So, how do you keep a tens-of-thousands-of-kilometers-long cable from crashing down? You have to use Newtonian mechanics to balance two forces: the gravity which is pulling down and centrifugal force which is pulling up. Here are the basics.
It’s an orbit where a satellite stays fixed over the exact same point on the planet’s surface. On Earth, this is Geostationary Orbit (aka GSO) at 35,786 km of altitude (quite an Eiffel tower!), where a full, circular orbit matches the Earth's 24-hour rotation. Oh, and by the way it works only above the Equator.
Let’s say you somehow stretched a 35,786 km long tether up to GSO. Congratulations! But simply anchoring a cable at the surface and dropping it from GSO simply won't work : gravity will yank it straight down. The good news is, there is a solution. Hint: you’ll need some extra thousands of kilometers of tether.The problem here is that no force is balancing G (Gravity). The tether falls on Earth.
To balance the cable you need to extend the tether past GSO into deep space and attach a heavy counterweight.
If balanced with millimetric precision, the counterweight "pulls upward" like a sling (centrifugal force) while Earth's gravity "pulls downward" (gravity), creating tension on the tether. The equilibrium point won’t be at the GSO station, but way above it.To sum it up, here’s the ‘forces equilibrium formula’:
Where: G = Universal Gravitational Constant ; M = Mass of the reference body (Earth) ; r = radius (distance from point to the center of mass of the planet) ; v = orbital velocity.
So if the idea is not new and the physics works, why don’t we have a Space Elevator on Earth? In the next diary, we’ll look at the nightmare logistics, the Gemini XI tether experiments, and why setting it up on the Moon changes everything.
--Ignacio, Mauricio, and Nicolas (Polar Motion)